Question: Which of these numbers is composite? ${3,\ 47,\ 57,\ 67,\ 71}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 3, 47, 67, and 71 each have only two factors. The factors of 57 are 1, 3, 19, and 57. Thus, 57 is the composite number.